1. Field of the Invention
This invention relates to a fluorescent display apparatus, and more particularly to a segment type fluorescent display apparatus which effects displays of numerals, letters and the like by a combination of bar-shaped segmented anodes.
2. Description of the Prior Arts
A fluorescent display apparatus is widely used as a display device in various electronic or electrical instruments, because it is a self-illuminating display device which can be driven at a relatively low voltage and is low in power consumption and excellent in luminous color. Phosphors which are the most commonly used in the conventional fluorescent display devices are ZnO:Zn system phosphors which emit green. Recently, a fluorescent display apparatus which can emit luminous colors of other than green is required in the various fields industry. In order to meet such a demand, phosphors for use in the fluorescent display apparatus other than ZnO:Zn phosphor have been developed and come into actual use, such as, for example, red emitting phosphors which are based upon a mixed conductive material with Y.sub.2 O.sub.3 :Eu, Y.sub.2 O.sub.2 S:Eu or YVO.sub.4 :Eu phosphor, a yellow emitting phosphor which is based upon a mixed conductive material with a ZnS:Mn phosphor or a blue emitting phosphor which is based upon a mixed conductive material with a ZnS:Ag phosphor.
In the prior art, there are several proposals for producing a numeral or character display apparatus which changes its display color responding to input signals within a single display apparatus by using the newly developed as well as the conventional ZnO:Zn phosphors.
FIG. 1 shows a display pattern of the conventional numeral or character display apparatus. The display pattern is composed of seven segmented anodes 1a to 1g (hereinafter referred to as a segment) which are arranged in the form of the figure "8" to form an inner display portion, and additional seven segments 2a to 2g arranged in close proximity to each of the segments 2a to 2g of the inner display portion to form an outer display portion. The inner and the outer display portions have deposited thereon phosphors of different luminous colors, respectively, thereby to form one display portion. In the display pattern shown in FIG. 1, spaces for connecting the segments 2a and 2b and the segments 2c and 2d are too wide, and the connecting portions of the segments 2g, 2b and 2c or the segments 2g, 2f, 2e are too unnatural. The digits displayed by the display pattern shown in FIG. 1 are less appealing and hardly legible. Therefore, it is not put to practical use.
As another approach, there is proposed a display pattern improving legibility of the display numerals and effecting the display in multicolors as shown in FIG. 2. In the display pattern shown in FIG. 2, one digit of the numeral display portion is composed of a pair of seven segments 3a to 3g and 4a to 4g, which are connected in common at each of the corresponding segments 3a and 4a, 3b and 4b, . . . , and 3g and 4g, thereby to form display portions 3 and 4. The segments 3a to 3g and 4a to 4g of the respective display portions 3 and 4 have deposited thereon phosphors of different luminous colors, and either of the display portions is energized and illuminated by selecting either a grid 5 or 6 depending upon an input signal. In the display pattern shown in FIG. 2, it is hard to make reading of the displayed numerals, because the numerals in the respective colors are displayed in different locations. This deteriorates space factor in the display apparatus. Furthermore, in a multi-digit display apparatus, the displays are hard to scan, because the display patterns are illuminated with wide spaces therebetween.
In the conventional fluorescent display apparatus of another type, a mixed phosphor made of two phosphors each having different luminous color is deposited on segments, and the phosphors are illuminated in the respective colors by changing anode voltage. This fluorescent display apparatus effects the luminous display by making use of the characteristics of the phosphors each having different threshold luminous voltage and driving voltage for effecting the illumination of sufficient brightness, however, the luminous color in this fluorescent display apparatus is unsatisfactory, because it is not pure.